Automatic telephone systems



Dec. 24, 1963 s A. c. CORNER 3 AUTOMATIC TELEPHONE SYSTEMS Filed May 2, 1960 13 Sheets-Sheet 1 SSM' Fig.1

| N V E N TOR 42 H? CAI 1P1 ES CaE/VER ATTORNEY Dec. 24, 1963 A. c. CORNER 3, 1

AUTOMATIC TELEPHONE SYSTEMS Filed May 2, 1960 13 Sheets-Sheet 2 SMCA SMCB

TRSiZi- TRS 140 TRS141 INVENTOR AATIM? $442455 ave/v52 ATTORNEY Dec. 24, 1963 r A. c. CORNER 3,115,553

AUTOMATIC TELEPHONE SYSTEMS Filed May 2. 1960 13 Sheets-Sheet 7 fnsu INVENTOR AFT/40'? CHARLES CaeNEE ATTORNEY Dec. 24, 1963 Filed May 2. 1960 A. C. CORNER AUTOMATIC TELEPHONE SYSTEMS 13 Sheets-Sheet 9 LPAA AA F5 ALBi LPAB ERSSB- ERS6B $2051 FIT ERSZ B iDB (secrz REG) ERSiB n4 1 H HlO E 105mm REG) INVENTOH: flETH/JR- CHAEL ES CQRNER} ATTORNEY Dec. 24, 1963 A. c. CORNER 3,115,553

AUTOMATIC TELEPHONE SYSTEMS ATTORNEY Dec. 24, 1963 A. c. CORNER 3,115,553

AUTOMATIC TELEPHONE SYSTEMS Filed May 2, 1960 13 Sheets-Sheet 12 m m m s N W R J H H H H l m IN. 5 JG %u JU .5 .5 km .5 5 M 2: Pt N": m; m J M m 1!. c m i 5 v. M a 3 E E a E E Q E E m wwiijij A 8 n Tswmksww N5 5 En 4 9% xmmn h H H H 0 lol m Nah NEH war 58 :3 58 :2 zwmsfl 28 58 5% EU 3 N5 NE NE 1- L1 1 3 1; 1 3 1 1 3 1 4. A. q m wfommh mnnw.om -fl 5 A8523 @5250 $55 3m ATTORNEY Dec. 24, 1953 A. c. CORNER 3,115,555

AUTOMATIC TELEPHONE SYSTEMS OJ'RS INVENTOR ARTHUR CHARLES CORNER BY I ATTORNEY United States Patent 3,115,553 AUTOMA'IEQ TELEPHONE SYSTEMS Arthur Charles Corner, Liverpool, England, assignor to Automatic Telephone & Eiectric Company Limited,

Liverpool, England, a British company Filed May 2, 196d, Ser. No. 26,297 Claims priority, appiieation Great Britain May 9, 1959 6 Claims. (Cl. 179-22) be used for a plurality of conversational connections simultaneously. Generally, systems employing link working are of a relatively involved nature from the trunking aspect, and often incorporate highly-centralised and complex common control equipment which derives digital information from registers, and processes that information for use in the direct control of switching stages to effect the setting-up of conversational connections.

The invention particularly relates to a crossbar-type telephone system which operates on what is known as the self-steering principle. According to this principle crossbar switch stages comprising link-connected primary and secondary switches are employed and a connection is set up between an inlet to the primary switch of one stage and an outlet of a secondary switch of another stage by marking all the available paths extending over the switching stages between the inlet and the outlet, by selecting one of the marked paths and by operating the switches of the stages to complete the connection over to selected path. For this purpose the inlets to a switch are each connected to a bridge and the outlets are multipled to corresponding crosspoints in all the bridges. The outlets to a switch each include a marking conductor which is not multipled to the crosspoints but terminates on a select magnet and the switch includes a marking relay which is operated when any select magnet is operated. The operation of the marking relay serves to apply a marking potential to the marking leads of all the available inlets to the switch and hence to the outlets of switches in the adjacent rank. Therefore, when a marking potential is applied to the marking lead of an outlet of a switch, the select magnet associated with the marking lead operates followed by the marking relay and the marking potential is applied to all the available outlets of the switch. Usually three conductors are multipled at each crosspoint through the switch, two being speech conductors and the third being the P conductor. When one of the marked inlets has been selected, a potential is applied to the P conductor to operate the associated bridge magnet thereby completing the connection between the selected inlet and the calling outlet in the well known manner of a crossbar switch. Bridge magnet contacts which are operated when the bridge magnet is operated disconnect the marking conductor of the associated inlet and thereby prevent marking potential being applied to a busy inlet.

In a typical exchange operating on the self-steering system and having subscribers lines terminated on the outlets of the primary switch of a line selector consisting of primary and secondary crossbar switches, the initiation of a connection by a subscriber causes all available paths between said primary switch and secondary switches linkconnected thereto to be marked, the marking being extended to all the inlets of the secondary switch to which the marked and available links have access. The inlets of the secondary switch are connected to originating trunks and terminating trunks and the terminating trunks have access to speech path relay sets. On a call origination marking potential is applied only to inlets connected to originating trunks which also have access to available speech path relay sets. The secondary switch is provided with means for selecting one inlet and for operating the bridge magnet of the selected inlet by applying a potential to the P conductor. On the closure of the relevant crosspoint, the potential on the P conductor is extended to the outlet relevant to the operated select magnet and thence over the link to operate the appropriate bridge magnet of the primary switch to connect the calling subscribers line to the selected speech path relay set.

A switching stage consisting of link-connected primary and secondary crossbar switches is provided between the speech path relay sets and the terminating trunks and the speech path relay sets have access to registers. The registers respond to dialled digits representing the called line and take into use one of a number of markers to which information designating the called line is transferred. The selected marker applies a marking potential to the called line circuit and if it is idle the marking is extended, in the manner described for the calling line, through the primary and secondary switches of the appropriate line selector to all available terminating trunks and thence over all available paths accessible to the available terminating trunks through the primary and secondary switches of the switching stage. The inlet to one particular primary switch of the switching stage has already been selected by the selecting of a speech path relay set and the bridge magnet relevant to this inlet is now operated and is followed by the operation of bridge magnets in the secondary switch of the switching stage and the primary and secondary switches of the line selector to complete the connection between the calling and called subscribers.

It will be understood that the above description gives onl ythe principles of operation in a self-steering system and that many features such as trunking details have been omitted. However, it is believed that sufiicient has been said to enable the self-steering principle to be understood.

The main object of the present invention is to provide an improved self-steering system in which the number of connections which may be set up simultaneously may be increased.

A further object of the invention is to provide an improved crossbar selector switch for use in the self-steering system.

Another object of the invention is to provide a crossbar switch the internal trunking of which provide an increased number of outlets.

According to a feature of the invention groups of subscribers line circuits are connected to different line selector divisions and each switching or trunking section is divided into two sub-sections by dividing the outlets of the primary switches into two groups and link-connecting the two groups of outlets to different secondary switches, each group of outlets providing routes to the terminating trunks of all the line selector divisions and the marking conductors of the routes including contacts of switching devices provided on the basis of one for each trunk subsection for each line selector division whereby simultaneous connections can be set up over the same switching section provided the connections are not for subscribers in the same line selector division.

Another feature of the invention relates to a crossbar switch selector having first and second groups of select magnets, an inlet connected to each bridge and multipled to crosspoints controlled by the first group of select magnets, two groups of multi-conductor outlets each including a marking conductor and a plurality of conductors multipled to corresponding crosspoints of all the bridges, two discriminating relays, one for each group of outlets, one of the discriminating relays being operated when an inlet is taken into use, the operation of a discriminating relay extending the marking conductors of the corresponding group of outlets to the first group of select magnets, one only of which operates in response to marking potentials applied to any of said group of outlets, a switching device for each select magnet of the first group, the switching device operating when the corresponding select magnet operates and serving to extend the marking conductors of outlets relevant to the operated discriminating relay and the operated switching device to the appropriate select magnets of the second group to operate one only of the select magnets relevant to one of the outlets of the group, the operation of the bridge magnet relevant to the inlet taken into use serving to connect the one inlet to the one outlet.

A further feature of the invention relates to a crossbar switch having a first group of three select magnets and a second group consisting of the remaining select magnets, a plurality of inlets each connected to one bridge and each being multipled to the operative contact pile-ups of crosspoints controlled by said first group of select magnets and a plurality of outlets arranged in sets of three and a set of not more than two, the diiferent sets of three outlets being connected to the contact pile-ups of the crosspoints controlled by all except one of the second group of select magnets while the set of two outlets is connected to the contact pile-ups of the crosspoints controlled by said one select magnet.

The invention will be better understood from the following description of the preferred method of carrying it into effect which should be read in conjunction with the accompanying drawings.

Of these drawings:

PEG. 1 shows in outline a crossbar switch arranged for triple-group working, FIGS. 2 to 5, when placed side-by-side in that order, form a trunking diagram appertaining to a typical 10,000 line automatic telephone exchange according to the invention,

FIGS. 6 and 7, arranged with FIG. 6 on the left, constitute the circuit of a first selector for use in the typical exchange,

FIGS. 8, 9, 10 and 11, when arranged with FIGS. 8 and 9 above FIGS. 10 and 11 form the circuit of a marker, together with auxiliary devices, for 500 subscribers line circuits served by one division of the typical exchange, and

FIGS. 12 and 13 are the circuits of a tariff computer and outgoing junction relay set respectively.

Crossbar Switches f the Selecting Stages In the automatic telephone exchange to be described, the selectors of the main selecting stages involve crossbar switches of the 12 x type i.e. having twelve select mag- The mechanism of the switch is of the conventional type such as described in the Bell System Technical Journal, volume XVIII, pages 80 to 86. As described in this article an individual axially-pivoted select bar, carrying a selecting finger for each bridge, is associated with each pair of select magnets such as ISM and 25M, 35M and 45M hSM and 3AM, 2AM and 1AM as shown in FIG. 1. The operation of a select magnet swings the select bar in the appropriate direction whereby the fingers are so positioned, with respect to corresponding crosspoints in each bridge, as to enable one of said crosspoints to be actuated by subsequent operation of a bridge magnet. In this conventional type of switch mechanism the crosspoint remains operated under the control of the operated bridge magnet when the select magnet has been released.

In the simplified illustration, each bridge is represented by three bridge commons (long vertical lines), and cooperating contact points (short vertical lines) are shown for each of the select magnets ISM to 98M and auxiliary magnets 1AM to 3AM. Each of the select magnets ISM to 83M have three cooperating contact points, one for each bridge common, whereas select magnet 98M has two cooperating contact points, the third being indicated in the drawing but not connected. Further the auxiliary magnets 1AM to 3AM each have only one coo erating contact point. Thus magnet 1AM has a contact point cooperating with the left bridge common of all the bridges, magnet 2AM has a contact point cooperating with the centre bridge common of all the bridges whereas magnet 3AM has a contact point cooperating with the right hand bridge common of all the bridges. It will be understood that using a conventional switch mechanism of the type previously mentioned, three cooperating contact points will be provided for select magnets 1AM to 3AM and 95M and in using the switch for the present invention the contact points which are not required can either be left unwired or removed. The removal of these contact points is the only way in which the switch when used with the present invention could diifer from the conventional mechanism.

From the simplified illustration of FIG. 1, it would appear that single conductor connections are effected by the switch. In fact, however, for the present type exchange, the path through arswitch involves three conductors, namely A and B (speech) and P (private) conductors. Accordingly the bridges actually have nine bridge commons and a similar number of contact points are provided at each of the crosspoints associated with select magnets ISM to 95M, Whereas three contact points are provided in each bridge for each of the auxiliary magnet crosspoints. It should be pointed out that each selector also includes a number of control relays, and that the inlets and outlets have one or more conductors other than those (A, B and P) which are capable of being connected through the switch.

The 26 outlets are multipled through all 10 bridges in the manner shown so that the outlets are associated with the crosspoints of select magnets ISM to 98M as follows:

Outlets Select Magnets nets and ten bridge magnets. As illustrated in simplified form by FIG. 1, each switch is arranged for what may be termed triple-group working so that each of the ten inlets I1 to 110 has access to as many as 26 outlets, G1 to 025, individually. The ten bridges BRT to BRltl are represented vertically, and the positions of references llSM to 98M are indicative of the effective positions of the nine select magnets with respect to the switch crosspoints which they control in each bridge, and likewise the references 1AM to 3AM, correspond to the effective positions of auxiliary select magnets with respect to other crosspoints in each bridge.

Outlets 1, 4, 7, 10, 13, 16,

Auxiliary Magnets 1AM 2AM 3AM To assist in an understanding of the arrangement of the switch, the method of establishing a connection between inlet I4 and outlet Old will be outlined. Firstly auxiliary magnet 1AM and select magnet 45M are operated and subsequently the bridge magnet of bridge BR4 is operated. The latter in conjunction with magnet 45M connects outlets 010, S11 and 012 to the three groups of bridge commons in bridge SR4, whereas the same bridge magnet in conjunction with magnet 1AM connects inlet 14 to the particular group of bridge commons to which outlet 010 is connected. Thus it can be seen that the switching principle is such that a select magnet ISM to 98M, operated in conjunction with a bridge magnet, connects three outlets to three groups of commons of the particular bridge, whereas an auxiliary select magnet 1AM to 3AM, having enabled an auxiliary crosspoint in the same bridge to be operated, efiects a selection whereby the inlet is connected to one of the three groups of commons and so to the particular outlet.

The switch would be controlled so that the auxiliary and select magnets are released immediately a connection has been set up, whereupon the connection is maintained solely by the operated bridge magnet. It will be appreciated that although the actual setting-up of connections through the switch must proceed on a one-at-a-time basis, each of the ten bridges may be occupied in respect of individual through-connections as the same time.

It will be observed that one group of contact points relevant to magnet 93M in each bridge is not wired and may be omitted since it is not available for use. It is not possible to use these contact groups to provide a twentyseventh outlet, because auxiliary magnet 3AM and select magnet 95M control the same select bar, and consequently both magnets cannot be operatively eifective at the same time.

The principle of triple-group working is not limited in application to an arrangement such as that shown in FIG. 1 where the outlets are multipled throughout the bridges. Indeed the particular switch could readily be arranged so that each inlet gives access to a difierent group of as outlets making a total capacity of 260 outlets.

General Description of Exchange The exchange will be described with reference to the trunking digaram comprising FIGS. 2 to 5 and which relates to a 10,000 line exchange. It should be understood that the crossbar switches of the selecting stages are arranged to be controlled in accordance with the previously described self-steering system and in the drawings the crossbar switches are represented by rectangles of which the vertical lines represent the bridges to which the inlets of the switch are connected whereas the horizontal lines represent the horizontal multipling of the outlets across the bridges. Only the first and the last of the bridges and multiplings are shown in order not to confuse the drawing.

The divisi0ns.The exchange comprises twenty divisions each individually serving 500 subscribers. One such division, DIVL is represented in the diagram and this involves a line-selector arrangement having twenty primary crossbar-switches selectors LS/PRI and eight secondary selectors LS/SEC, only the first and last switch of each set being represented for simplicity. Each of the switches is internally wired in accordance with FIG. 1 to provide ten inlets and 25 outlets, the 26th outlet not being used. Each switch has a group of control relays individually associated with it but for convenience they are not represented. The 500 subscribers lines SL are connected over the main distribution frame MDP and line intermediate distribution frame LIDF to individual subscribers line circuits SLC which are terminated in groups of 25 upon the outlets of the twenty primary selectors, so that each group is served by a particular selector. The 200 outlets of the eight line-selector secondary switches are individually connected to the corresponding number 6 of primary selector inlets over 200 links LKS in such a manner that each secondary selector is connected to each primary selector by at least one link, and in some cases two links. The link working arrangement gives each group of 25 subscribers, accommodated by a primary selector, access over ten links to all eight secondary selectors.

As regards the inlets of the eight secondary selectors LS/StECJl to Ins/SE68, the first five inlets (bridges BR l to 8R5) of all selectors are taken by way of 40 so-called terminating trunks TTl rto "[140 to a strapping field SPA, whereas the remaining 40 inlets of the secondary selectors (involving bridges BR6 to BRlll) are taken over 40 originating trunks OT to the trunk distribution field TDF. The latter is common to the exchange, and accordingly the 40 originating trunks of each of the remaining divisons DIVE-DIVZQ are also connected to it.

The terminating trunks are concerned with calls incoming to subscribers of the division whereas the originating trunks are used for ca lls originated by subscribers of the division. It will be noted that a stant shift circuit SSC is associated with the different groups of secondary switch inlets relevant to originating trunks, the immediate eiiect of this circuit being to give some measure of equalisation in respect of the usage of the secondary switches of the division so that a corresponding effect may be obtained as regards the distribution of traffic to the socalled trunk sections of the exchange to be described later.

Each division of the exchange incorporates a SOO-line marker such as MKR and an associated pair of entry relay sets 'ERSlA and ERSIB, ERSZA and ERSZB and so on for each of the trunk sections of the exchange. The 500 marking wires emanating from the marker are individually connected to corresponding conductors at the numerical side of the line intermediate distribution frame LIDF whence they are extended to individual line circuits.

The trunk sections.The number of so-called trunk sections is determined by trafiic requirements, and in the present case it may be assumed that six are provided, one of which, designated SECT 1, is represented in the trunking diagram.

The sections, which incorporate first and second crossbar selectors, transmission relay sets, first and second choice registers and register-allotters, constitute the intermediate portion of the exchange from the point of view of switching, all the sections being accessible from and giving access to every SOO-line division.

Considering the selecting stages of the typical section, one stage comprises sixteen first selectors 181 to 1316, and the other stage involves vtwo groups of ten second selectors, one embracing selectors ZSAG. to ZSAltl, and the other embracing selectors 2SB1 to 281310. The first and second selectors each incorporate a crossbar switch together with its necessary conltrol relays, the crossbar switch being arranged in the manner [represented by FIG. 1. Again, although the switch is adapted for the throughswitching of A, B and P wires, the inlets and outlets involve one or more other conductors for control purposes.

The ten inlets of all first and second selectors are available for use, and likewise all 26 outlets of each of the second selectors are available whereas only 25 outlets of the possible 26 are used in the case of first selectors.

The section has transmission relay sets 1TRS1 to 1TRS160 which, like corresponding relay sets of other sections, have their calling sides connected by individual trunks to the trunk distribution frame TDF. The relay sets incorporate speaking battery feeding and called subscriber answering supervision arrangements and are equipped to control the transmission of ringing current to called subscribers lines of the exchange, and to control the transmission of ringing tone, busy tone and N.U. (number unobtainable) tone to calling subscribers as required. Moreover another important function of the relay set is to extend positive-battery metering pulses over the calling side P Wire for call fee purposes.

The 160 tnansmission relay sets of each trunk section are allocated as required for locally originated calls, for incoming junction calls of various kinds, and for service calls such as those from a test desk.

2nd choiceregisters Transmission relay sets sREGl TRSl-TRS40 2REG3 TRS il-TRSEO TRSSl-TRSlZO The transmission relay sets are arranged in groups of ten and each group is connected to the ten inlets of a particular first selector. Thus relay sets TRSl. to TRSltl' are connected to inlets 1 to 14 respectively of selector 1S1, relay sets TRS11 to TRSZMP are related to inlets 1 to respectively of selector 152, and so on to relay sets TRS151 to TRSlfit) which are terminated upon inlets 1 to 10 of selector 1816. Now the first selectors are arranged in pairs 1S1 and 182, 133 and 154 1815 and 1816, and the outlets of the selectors of each particular pair are multipled so that 25 outlets are derived from (the two selectors together. These are divided into what may be called A outlets and B outlets and are designated 180A and ISOB in the trunking diagram. It will be recalled that the selector crossbar switches cater for 26 outlets, but in the case of first selectors only 25 are used. More particularly if we consider the pairs of selectors as numbering 1 to 8 downwardly, outlet number 26 of the odd pairs and outlet number 25 of the even pairs are not used. Considering selectors 151 and 152, which are typical of the odd pairs, the twelve outlets 1, 2, '3, 7, 8, 9, 13, 14, 15, 19, 2d and 21 are multipled and constitute A outlets, whereas the thirteen outlets 4, 5, 6, 10, 11, 12, 16, 17, 18, 22, 23, 24 and 26 are also trnultipled together and constitute the "B outlets. On the other hand as regards the even pairs of selectors, such as selectors 1815 and 1816, the multipled outlet number 25 makes an additional A outlet whereas the B outlets are reduced to twelve by the omission of outlet number 26.

It will be seen that 100 A outlets (150A) and 100 B outlets (ISOB) are derived from the rank of first selectors, the A outlets extending over links ALKS are terminated on the 100 inlets of the ten second selector 218A, while the B outlets extend to the 10% inlets of the ten selectors ZSB. The distribution of the first selector outlets is such that each first selector, and therefore the relevant ten transmission relay sets, has access to every secondary over one link and in some case over two links.

The secondary selectors ZSAI and ZSAlt) provide outlets to a total of 260 trunks, and the selectors 2531 to 2SB10 have a similar outlet capacity. Of each of the outlet groups, 200 designated LOA and LUB are available for locally terminated calls and 60 designated JOA and JOB are available for outgoing junction calls. The individual transmission relay sets have access to all 520 secondary selector outlets.

The provision of A and B outlets at the first selectors, and the connection of those outlets over A and B links (ALKS and BLKS) respectively to different groups of second selectors each giving access to a different group of local (LOA or LOB) and outgoing junction (JOA or JOB) outlets, in elfect divides the section into two sub-sections, and it may be convenient to refer to that embracing second selectors ZSA as sub-section A, and to that embracing second selectors ZSB as sub-section B. The particular sub-section to be used in the setting-up of a connection from a transmission relay set to a Wanted local subscriber or to an outgoing junction, is determined by a discriminating condition applied to the first selector.

The section has sixteen first-choice registers 11.11661 There are sixteen register-allotters in the section, designated RA1 to RA16, and each is associated with ten transmission relay sets of a group and with the first selector serving the group, the principal function of the allotters being to control the access paths of the first and second choice registers. Typically register-allotter M1 is concerned with the access paths to registers lREGl and ZREGI from the ten transmission relay sets TRS l to TRSlO. The register-allotter is also concerned in the connection of the discriminating condition, previously mentioned, to a first selector to determine whether subsection A or B is to be used for a call.

The registers are arranged to store dialled digits in any convenient manner, and have access, as and when required on calls to other exchanges, to groups of local senders LS, national senders NS and tariff computers TC. All of these equipments (for instance 24- of each type) are accessible over multi-conductor paths by way of the trunk distribution frame TDF and may, if required, be common to the whole exchange.

The local and national senders may be arranged for exchange-code translation and would be adapted to transmit digits over outgoing junctions in accordance with the route involved. Thus in all probability the local senders, which are concerned with the setting-up of calls to other exchanges in the local multi-exchange network, would transmit conventional loop impulses at 10 i.p.s., whereas the national senders might well be arranged to select one of several modes of digital transmission, which may be for instance 10 or 50 i.p .s. loop impulsing or some form of coded voice-frequency transmission.

The tariff computers would be arranged to be taken into use individually on outgoing junction calls, whereupon the setting of a tariff computer by a register in accordance with the call route, determines which of a plurality of tariff signals is duly to be transmitted to the outgoing junction relay set used for the call.

The trunking section also includes two section marking control circuits SMCA and SMCB which are concerned with sub-sections A and B respectively. Both of these circuits are accessible from all registers of the section and when any register has received all the digits necessary for the completion of a call, either for local termination or outgoing, it in effect applies to both section marking control circuits for permission for the call to proceed. If neither of the control circuits are in use when a register institutes a demand, either one of them may be seized and give the necessary permission, whereas if either one of them is busy the other becomes operative, but if both are busy the register will wait until a control circuit becomes idle.

The granting of permission for a call to proceed by section marking control circuit SMCA decides that subsection A is to be used for the call, and likewise section marking control circuit SMCB determines that subsection B is to be used.

The registers of the typical section are able to control the SOO-line marker of any division for the completion of calls destined for subscribers served by the exchange. Two multi-conductor digit-transfer paths, TPA and TPB, which are concerned with this function are commoned to all registers of the section, the first path being appropriate to calls to be routed over sub-section A, and the second path is used for calls over sub-section B. Each path comprises 25 conductors, five for hundreds digit indications, and ten each for tens and units digit indications. The two transfer paths of the section are directed to all twenty SOC-line divisions DIVE to DIVZtl by way of the strapping field SFA. The pair of digit-transfer paths TPA and TPB from each of the six sections is terminated in each division, the latter being provided with a marker entry relay set (ERSlA, ERSIB ERSfiA, ERSfiB) for each section.

Two other groups of conductors DA and DB (20 conductors each), also concerned with local calls using subsections A and B respectively, are commoned to all the registers of the section, these being one conductor of each group connected to each division. Thus of the twenty DA and DB conductors emerging from section SECT 1, TBA and IDB extend to division DIVl to control marker entry relay sets ERSlA and ERSllB respectively, whereas the pairs of conductors ZDA and 2DB NBA and ZtlDB are extended in a similar manner to control entry relay sets ERSlA and ERSlB, in divisions DIVZ to DIVZt) respectively. The DA and DB conductors from the other sections, SECTZ to SECT6, are also connected to appropriate entry relay sets (ERSZA, ERSZB ERSfiA, ERStEB) in the 20 divisions.

it may be mentioned briefly that the marking of one of the twenty DA or DB conductors by a register, effectively chooses the SOD-line group of wanted subscriber, i.e., the particular division, whereas the energisation of three conductors (hundred, ten and unit digits) of the relevant 25-conductor transfer path T PA or TPB defines an individual subscriber in the division.

It is important to note that if a sub-section A is to be involved in a call, one of the DA conductors and transfer path TPA are used for defining a called subscriber, but if a call is to utilise sub-section B a DB conductor and transfer path T PB will be employed. It will be shown that this arrangement enables the section to institute the marking of a subscribers line circuit in each of any two divisions concurrently, and moreover settingup of connections from those line circuits to the transmission relay sets concerned may also proceed and be completed concurrently over the separate sub-sections without mutual interference. However if the calls involve transmission relay sets terminated on inlets of the same e.g. exchange code digits, passed to it by the register. This selecting function effects operation of a so-called junction marking relay relative to the sub-group of the required junction route. Thus discriminator I RDA may selectively operate one of a set of junction marking relays, HMA, ZlMA and the like, to establish the necessary connections (additional to the A, B and P Wires which are permanently connected) between the outgoing junction relay sets, such as OlRS-lA, of a particular subgroup and the relevant ones of those second selector outlets of sub-section A and collectively designated JOA. Similarly discriminator JRDB would be used to selectively operate one of a second set of junction marking relays, IJMB, 21MB and so on, to complete additional connections between relay sets, such as OJRS-lB of the required second sub-group, and the relevant ones of second selector outlets JOB of sub-section B.

Each section would have under its control, a number of pairs of junction marking relays corresponding to the number of junction routes, to permit any sub-group of junctions to be associated with any sub-section.

The operation of any junction marking relay by completing additional connections (marking and test wires) between junction relay sets of a sub-group and a particular sub-section, will in effect permit an idle one of those junction relay sets to be selected for use.

The splitting of each junction group into two subgroups as outlined, will enable the settingup of an independent connection to be initiated to a junction relay set of each sub-group simultaneously by Way of partner sub-sections or complementary sub-sections in different sections. The only exception is when the calls involve transmission relay sets served by the same first selector, in which case the junction connections are set-up successively.

Originating franks-As already mentioned each subscribers division has originating trunks which enable a subscriber to be connected to a transmission relay set in any section when he originates a call. The 40 originating trunks of each division are terminated upon a trunk distribution frame TDF, and each group of 40 is distributed as equally as possible, by jumpering, to all the sections. Thus in the present exchange, the 40 originating trunks of division DIVI might well be distributed over the sections as follows:

N0. of trunks.

Section 7 1 7 7 6 6 SECTl SECTZ SECT3 SECTi SECT5 SECTG first selector the calls would be completed consecutively.

The typical exchange illustrated in outline in the trunking diagram caters for outgoing junction calls, and for this purpose each section incorporates a pair of junction route discriminators such as J RDA and JRDB. The junctions 0] of each outgoing route are divided into two sub-groups which are preferably equal and one of which is accessible from transmission relay sets over sub-section A and the other over sub-section B of each section. Each pair of junction route discriminators of a section is aocessible from all the registers of that section, and, in the typical section shown, discriminator lRDA is taken into use when a caller, having taken a transmission relay set into use, requires to be connected to one of the subgroup of junctions, of any route, served by sub-section A, whereas discriminator JRDB is used for connections to one of any sub-group of junctions served by sub-section B. Briefly if section marking control circuit SMCA is seized by a register, and the digital information stored by a register is indicative of an outgoing junction call, it is determined that discriminator IRDA is to be used. Likewise section marking control circuit SMCB would determine that discriminator JRDB would be used.

It may be mentioned that when a discriminator is taken into use on an outgoing junction call, it performs a selecting function in accordance with routing information,

It would also be preferable to have the individual trunks of each of the groups accessible from different secondary selectors of the division. Since the five originating trunk inlets of each secondary selector (bridges 6 to 1d) are arranged for a particular order of choice, it may also be advantageous to have the individual trunks of a group dispersed over a range of choices of inlets.

Considering the 160 transmission relay sets in each section, of the order may for instance be allocated for use on locally originated calls and these are connected to individual originating trunks from all divisions. Taking the group of 6 or 7 trunks extending from a particular division into a section, these would preferably be spread over a corresponding number of transmission relay sets in such a manner as to make the maximum number of first choice and second choice registers available to them. Certainly the originating trunks of a group would be connected to transmission relay sets served by different first selectors and first choice registers.

The exchange would cater for incoming calls over junctions H from various types of exchanges. Accordingly groups of incoming junctions from automatic, manual and trunk exchanges, and respectively designated AA, MAN and TR, are connected to the trunk distribution frame TDF for distribution to transmission relay sets in appropriate sections. If required one or more trunk l l sections may be used exclusively for incoming junction calls. Trunks TD from the test desk are also connected to transmission relay sets by way of trunk distribution frame.

Terminating trunks.It will be recalled that each section has 520 second-selector outlets and of these 400 are to give access to terminating trunks of all twenty divisions for the purpose of completing calls to subscribers of the exchange. Of the second-selector local outlets, 200 collectively designated LOA and 200 designated LOB are obtained from sub-sections A and B respectively. Ten LOA and ten LOB outlets from each of the six sections SECTI to SECT6, making a total of 120 and extending over strapping fields SFB and SPA are connected to the 40 terminating trunks TT-l to TT40 of the typical division, so that each terminating trunk is connected to three second-selector outlets.

The links between second-selector outlets and terminating trunks embrace four conductors of which three, name- 1y, and P conductors, are continuous whereas the fourth, which is a marking wire M, is normally broke by a make contact of a terminating trunk marking relay lTTMA, ITTMB dTlMA, dTTMB. Each such marking relay has ten contacts one of which is shown for simplicity, and the prefix digit of the relay designation is indicative of the section to which it is related whereas the sufiix letter A or B is indicative of the relevant sub-section. Thus the ten contacts of relay TTTMA, when operated, would complete the marking paths of the ten links between sub-section A of section SECTl and ten terminating trunks of division DlVl, and likewise relay ITTMB is concerned with the completion of the marking paths of the ten links between sub-section B of section SECTl and the same division. The remaining five pairs of relays are related to other sections and the same division in a similar manner.

It will be appreciated that a group of six pairs of terminating trunk relays, such as those represented in the drawings, are provided for each SOC-line division. Each of the twelve marker entry relay sets ERSIlA to ERS6B of a division is arranged to control the operation of an individual terminating trunk marking relay. Thus for example, if a caller, who has taken into use a transmission relay set in section SECTl, requires connection to a subscriber served by division DIVE, and it has been estab lished that the connection is to be completed over subsection A, relay set ERSTA is used to gain access to the divisional marker, and that relay set determines that relay 1TTMA shall operate. Since only one entry relay set of the particular division can be operative at any one time, it follows that only one terminating trunk marking relay relevant to that division can be operated, relay lTTMA being operated in the present case. Therefore the marking (M) paths of the links between the calling subsection and the required division are completed, and the eliect of this is to enable a connection to be set-up between the calling transmission relay set and the wanted subscriber over an idle one of the available links.

The provision of pairs of terminating trunk relays between each trunking section and each SGO-line division ellectively completes the separation of each section into its two sub-sections. As a result of this it becomes more evident that it will be possible for each section to handle the setting-up of two calls to subscribers in dit ferent divisions simultaneously. It will also be appreciated that, as regards a particular section, one sub-section may be used for the process of setting-up of a connection to an outgoing junction relay set while the other is being used for setting up a connection to a local subscriber over a division. In both cases there is again the proviso that the two calls must not involve transmission relay sets served by the same first selector.

Exchange Subscriber Origi/mtes a Call The process of connecting a subscriber to a transmission relay set and register is in many respects substantially the same as was described in British specification No. 739,905 and will now be outlined with reference to the trunking diagram comprising FIGS. 2 to 5.

As already mentioned the 500 subscribers line circuits SLC of a division are terminated upon individual outlets of the 20 primary line-selector LS/PRI. When a subscriber originates a call, the loop applied to his line SL operates the line relay of the relevant line circuit in conventional manner. The ellect of this is to operate within the particular primary switch, a discriminating relay to signify that a call origination, as distinct from an incoming call, is to be dealt with and accordingly an originating call indication is connected to the discriminating lead of the ten links terminated on the primary switch. It should be mentioned that each link comprises five conductors viz: A, B, P, D (discriminating) and M (marking). The discriminating relay is also effective in causing the start shift circuit SSC, associated with all the secondary line selectors LS/ SEC of the division, to prepare for the testing of the 40 originating trunks of the division in successive groups or" live from a pro-allotted point. The operation of the subscribers line relay also results in the operation of the auxiliary and select magnets appropriate to the primary line-selector outlet serving the calling subscriber, and moreover causes said selector to apply a marking potential to those M wires of the ten links which are not already occupied on calls. The operated primary line-selector bridge magnets elated to busy links would prevent marking of busy links. At this juncture, the primary selector is adapted to prevent the operation of its other select and/or auxiliary magnets if another of its subscribers should originate a call or be called, and additionally the calling subscriber is guarded against intrusion from the 500-line marker (incoming calls) by a gnar ing earth which is extended by way of the line circuit to the relevant incoming marking conductor.

Now the ten links, emerging from the primary selector concerned in the present call, are distributed over all the secondary selectors, so that six of the secondary selectors are each connected to the primary by a single link whereas the remaining two secondary selectors each have two links to the primary. As already mentioned the idle links are defined by a potential applied to the relevant marking (M) leads. Taking any secondary selector which has one link marked, the marking is effective in operating the appropriate auxiliary magnet and this enables (a) an originating-call discriminating relay to be operated by the significant potential received over the discriminating conductor of the link and (b) the select magnet appropriate to the link to be operated from the potential on the M wire. It may be mentioned that the circuit arrangements of the secondary selectors are such that if more than one link to the same selector are marked, one of them is given priority in that the auxiliary and select magnets appropriate to it alone are operated. Therefore a single auxiliary magnet and a select magnet are operated in each of the marked secondary selectors.

The five inlets (6 to it) relevant to originating trunks, of each of the secondary switches of the division would be provided with individual testing relays for the purpose of detecting oiginating trunks associated with idle transmission relay sets having idle registers (first-choice registers initially) available to them. The group of .ve test ing relays in each secondary selector are arranged for a particular order-of-choice as regards their operation and if two encounter suitable transmission relay sets, the choice corresponds to the number order of the inlets. The eight groups, comprising the testing relays of all the secondary selectors of the division are arranged so that, if need be, those included in marked secondary selectors may be brought into a testing condition group-by-group until all of them are so conditioned. For this purpose the groups are in effect formed into a one-way closed chain, and, for trafiic distribution purposes, a different start lead from the previously-mentioned start shift circuit is introduced at the commencement of each group. The start shift circuit is virtually an eight-way cyclic distributor which advances one step each time any line selector primary switch is taken into use, and thereupon applies a starting condition to the appropriate point in said closed chain. This would cause the earliest succeeding group of testing relays appropriate to a marked secondary lineselector to proceed with testing of transmission relay sets. If all of the latter are busy and/or have no first-choice registers available for use, than after a few milli-seconds delay, the group of testing relays of the next marked selector begin testing. This procedure would be repeated until an idle and suitable transmission relay set is encountered, or, if no such relay set is encountered, until all the testing relays of the marked secondary selectors are in the testing condition.

Assuming that an idle transmission relay set having access to an idle first-choice register is encountered, the appropriate testing relay is operated by an idle-marking condition extending from the register by way of said relay set. The operated testing relay stops any further testing, guards the relay set and register against intrusion and operates the bridge magnet corresponding to the secondary switch inlet concerned. The seized transmission relay set is now associated exclusively with the first-choice register.

It is to be noted that when a first-choice register has been taken into use by a calling transmission relay set, the appropriate second-choice register, if idle, will be made available to the remaining idle ones of the same group of ten relay sets by the associated register-allotter. Thus in the course of a testing cycle such as that described, idle transmission relay sets with idle secondchoice registers may be encountered by testing relays of the secondary line-selectors. However the condition produced by second-choice registers and initially encountered by the relevant testing relays is dilferent to the idle marking condition produced by first-choice registers, and does not eii ect operation of the testing relay. Accordingly the testing cycle continues with the object of seizing the first available transmission relay set with an idle first-choice register.

Meanwhile any testing relay upon being extended to an idle second-choice register, although remaining inoperative itself, initiates operation of a relay having an operate lag which is a few milli-seconds in excess of the period required to perform the aforesaid testing cycle. If this cycle is completed without an idle transmission relay set and first-choice register being encountered, the operation of one of said slow-to-operate relays in a second-choice register will mature, whereupon the potential on the test conductor is made suitable for the operation of the relevant testing relay in a secondary selector. This would disable all other testing relays, guard the relay set and register against intrusion, and operate the bridge magnet of the appropriate second selector inlet.

It is now evident that when a subscriber originates a call, he causes all idle secondary switches to be marked and taken into use for the purpose of obtaining a transmission relay set and register over one of the 40 originating trunks OT which give access to all sections SECTI to SECT6. When a suitable relay set and register have been selected by the exclusive operation of a testing relay in one of the secondary line-selectors, the operation of the relevant bridge magnet in the secondary line-selector performs the following main functions; (a) enables the transmission relay set to extend additional conductors, A, B, H (holding) and P, of the originating trunk to the register, and (b) in conjunction with select and auxiliary magnets appropriate to the marked outlet of the secondary line-selector closes those crosspoints which now connect the A, B and P wires of the defined originating trunk to said outlet and thence over the link to the appropriate inlet of the calling primary line-selector.

At this juncture the testing relay in the secondary lineselector is released, the transmission relay set and register are busied-out, and the bridge magnet is held from the register until such time as this function is eventually taken over by the transmission relay set, as it would be when the register is duly released. Also at this time, in the register, a circuit element, which is to be concerned with (a) testing the continuity of the speech path which is to be set up to the calling line circuit and (b) determining the class-of-service to be accorded to the caller, is connected to the A and B conductors.

Now that the A, B and P conductors of the particular originating trunk have been connected over a link to the inlet of the calling primary selector, the potential advanced over the P conductor enables the bridge magnet relevant to the inlet to operate. Thereupon the bridge magnet, in conjunction with the operated auxiliary and select magnet defining the calling line circuit actuates crosspoints in the primary selector to connect the A, B and P conductors of the link to said subscribers line circuit.

At this stage the register, for a short period, tests for the continuity of A and B conductors to the subscribers line circuit, and, if the speech-path conductors are in order, determines, in accordance with potentials provided by the line circuit, which class-of-service is to be accorded to the caller. Moreover the register effects operation of the conventional cut-on relay in the line circuit by way of one of the speech conductors, and this releases the line relay and completes the connection to the subscribers loop. The cut-off relay is then held from the same source as the operated bridge magnets, and when the line relay releases, all the select and auxiliary magnets, which were operated by the present call origination, are released and moreover the relays in the various selectors revert to their normal conditions in readiness for other calls. The connection between the subscribers line circuit and the transmission relay set and register is held by the calling subscribers loop, the relevant bridge magnet in the primary and secondary line selectors, together with the line circuit cut-off relay, remaining operated from the register for the time being. In the meantime the dialledimpulses-accepting relay in the register is connected to the A and B conductors and dial tone is made audible to the caller by the register.

Call to Local Exchange Subscriber It will be assumed that a local subscriber, having initiated a call, has taken into use a transmission relay set and register, say TRSIO and llREGl respectively, in section SECTI of the exchange, and requires a subscriber served by division DIV}. he caller, upon hearing dial tone transmitted by the register, proceeds to dial the digits defining the wanted party. The digits are stored by the register, and when all of them have been received, register takes either one of the section marking control circuits, SMCA and SMCB, into use arbitrarily. The control circuit so taken into use thereupon grants permission for the procedure of marking the called subscribers line circuit to commence. Control circuit SMCA. would determine that sub-section A (involving second selectors ZSAl to ZSAitl) be employed, whereas control circuit SMCB would determine that sub-section B (involving second selectors ZSBI to 28316) be utilised.

Assuming that section marking control circuit SMCA is concerned in the present call, the register (lREGl) is enabled to pass a sub-section A discriminating signal by way of the register allotter RAE to the first selector (1S1) upon which the transmission relay set (TRSitl) is terminated. The A discriminating signal is effective in conditioning the particular first selector alone to be eventually responsive only to a backward marking potential received at one of its lSOA outlets. Thus the marking (M) wires of the twelve section A outlets alone are suitably directed within selector 151, the par- 

1. IN AN AUTOMATIC TELEPHONE EXCHANGE, A CROSSBAR SWITCH SELECTOR HAVING A PLURALITY OF BRIDGES, A FIRST GROUP OF SELECT MAGNETS, A SECOND GROUP OF SELECT MAGNETS, A PLURALITY OF BRIDGE MAGNETS, A PLURALITY OF MULTI-CONDUCTOR INLETS, ONE FOR EACH BRIDGE, EACH INLET BEING MULITPLED TO CROSSPOINTS INDIVIDUALLY CONTROLLED BY SAID FIRST GROUP OF SELECT MAGNETS, A PLURALITY OF MULTI-CONDUCTOR OUTLETS DIVIDED INTO TWO GROUPS, EACH OUTLET HAVING A MARKING CONDUCTOR AND A PLURALITY OF CONDUCTORS MULITPLED TO CORRESPONDING CROSSPOINTS OF ALL THE BRIDGES, THE MULTIPLED CROSSPOINTS SERVING AT LEAST TWO OUTLETS, TWO DISCRIMINATING RELAYS, ONE FOR EACH GROUP OF OUTLETS, MEANS RESPONSIVE WHEN AN INLET OF THE SELECTOR IS TAKEN INTO USE FOR OPERATING ONE ONLY OF SAID DISCRIMINATING RELAYS, MEANS RESPONSIVE TO THE OPERATION OF SAID ONE DISCRIMINATING RELAY FOR EXTENDING THE MARKING CONDUCTORS OF THE OUTLETS RELEVANT TO SAID ONE DISCRIMINATING RELAY TO SAID FIRST GROUP OF SELECT MAGNETS, AND FOR OPERATING ONE OF SAID FIRST GROUP OF SELECT MAGNETS IN A MUTUALLY EXCLUSIVE MANNER IN RESPONSE TO THE APPLICATION OF MARKING POTENTIALS TO ANY OF THE SAID OUTLETS RELEVANT TO SAID ONE DISCRIMINATING RELAY, A SWITCHING DEVICE ASSOCIATED WITH EACH MAGNET OF SAID FIRST GROUP OF SELECT MAGNETS AND OPERATED WHEN THE ASSOCIATED SELECT MAGNET IS OPERATED AND MEANS RESPONSIVE TO THE OPERATION OF ANY ONE SWITCHING DEVICE FOR EXTENDING THE MARKING CONDUCTORS OF THE OUTLETS RELEVANT TO SAID ONE DISCRIMINATING RELAY AND RELEVANT TO THE OPERATED SWITCHING DEVICE TO THE APPROPRIATE MAGNETS OF SAID SECOND SET OF SELECT MAGNETS AND FOR OPERATING IN A MUTUALLY EXCLUSIVE MANNER ONE SELECT MAGNET OF SAID SECOND GROUP OF SELECT MAGNETS RELEVANT TO ONE OF SAID LAST MENTIONED OUTLETS WHEREBY THE OPERATION OF THE BRIDGE MAGNET RELEVANT TO SAID ONE INLET SERVES TO CONNECT SAID ONE INLET TO SAID ONE OUTLET. 